Trials of Near-Surface Geophysics at Archeological Sites in SE Louisiana
The Louisiana Geological Survey, in coordination with Louisiana State University, conducted a series of geophysical surveys at archeological sites in the gulf coast region of southeastern Louisiana to evaluate instrument and field technique performance in densely-vegetated, organic-rich, water-saturated, and nonconsolidated sedimentary substrate. Test measurements of magnetic field intensity and electrical resistivity over appropriately sized and spaced sampling grids at 19th century sites in the Baton Rouge–New Orleans area aimed to detect known or suspected anthropogenic features. Magnetic gradiometer data successfully resolved artifacts in these settings, such as subsurface occurrences of building foundations, steel or iron objects, and cemetery burials. Electrical resistivity and induced polarization data also resolved cemetery burials and abandoned pathways, depending upon electrode array configuration.
Both field methods have strengths and weaknesses that are significant to investigation in the Louisiana coastal setting. Measurements using the proton precession magnetometer are not affected by water table level and the raw data require minimal processing. However, the instrument does not differentiate between artifacts versus irrelevant modern steel clutter from over two centuries of human habitation. The 4-electrode electrical resistivity survey is less sensitive to small isolated objects and can resolve stratigraphic horizons, but is impacted by ground water and the data typically require processing. Nevertheless, application of both instruments constitutes a valuable component of archeological exploration. Continued development of field and data processing techniques will broaden application to settings with fewer interpretive constraints, making them attractive tools for inexpensive and noninvasive exploration of archeological sites, particularly when applied in conjunction with archeological observations and expertise.
AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015